【OpenGL】三角形

2022-08-05 09:52:07

步骤

初始化顶点数组对象VAO
分配顶点缓冲对象VBO
将顶点数据载入缓冲对象中 glBufferData()
链接顶点属性 glVertexAttribPointer（指定了顶点着色器的变量与我们存储在缓冲对象VBO中数据的关系）

顶点数组

GLfloat vertices[] = {

    -0.5f, -0.5f, 0.0f,

    0.5f, -0.5f, 0.0f,

    0.0f, 0.5f, 0.0f

};

因为是3D坐标，所以有三个轴(x,y,z)，三个轴范围在-1~1之间。这里统一将z设为0，这样三个点的深度为0，所以看起来就是2D平面上的三角形。

顶点缓冲对象VBO

GLuint VBO;

glGenBuffers(1, &VBO);

glBindBuffer(GL_ARRAY_BUFFER, VBO);  //把缓冲绑定到GL_ARRAY_BUFFER上

glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); //复制顶点数据到内存

glBufferData是一个用来把用户定义数据复制到当前绑定缓冲的函数。它的第一个参数是我们希望把数据复制到上面的缓冲类型：顶点缓冲对象当前绑定到GL_ARRAY_BUFFER目标上。第二个参数指定我们希望传递给缓冲的数据的大小（字节）；用一个简单的sizeof计算出顶点数据就行。第三个参数是我们希望发送的真实数据。

第四个参数指定了我们希望显卡如何管理给定的数据。有三种形式：

GL_STATIC_DRAW：数据不会或几乎不会改变。
GL_DYNAMIC_DRAW：数据会被改变很多。
GL_STREAM_DRAW：数据每次绘制时都会改变。

顶点着色器

#version 330 core   //版本声明，opengl3.3

layout (location = 0) in vec3 position;

void main()

{

    gl_Position = vec4(position.x, position.y, position.z, 1.0);

}

编译

GLuint vertexShader;

vertexShader = glCreateShader(GL_VERTEX_SHADER);

glShaderSource(vertexShader, 1, &vertexShaderSource, null);

glCompileShader(vertexShader);

//错误检查

GLint success;

GLchar infoLog[512];

glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);

if(!success)

{

    glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);

    std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;

}

像素着色器

#version 330 core

out vec4 color;

void main()

{

    color = vec4(1.0f, 0.5f, 0.2f, 1.0f);

}

编译

GLuint fragmentShader;

fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);

glShaderSource(fragmentShader, 1, &fragmentShaderSource, null);

glCompileShader(fragmentShader);

着色器程序

GLuint shaderProgram;

shaderProgram = glCreateProgram();

glAttachShader(shaderProgram, vertexShader);

glAttachShader(shaderProgram, fragmentShader);

glLinkProgram(shaderProgram);

glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);

if(!success) {

    glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);

    ...

glUseProgram(shaderProgram); //将着色器对象链接到程序

//删除着色器对象

glDeleteShader(vertexShader);

glDeleteShader(fragmentShader);

}

VAO

// ..:: 初始化代码 (一次完成 (除非你的物体频繁改变)) :: ..

// 1. 绑定VAO

glBindVertexArray(VAO);

// 2. 把顶点数组复制到缓冲中提供给OpenGL使用

glBindBuffer(GL_ARRAY_BUFFER, VBO);

glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

// 3. 设置顶点属性指针

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid * )0);

glEnableVertexAttribArray(0);

//4. 解绑VAO

glBindVertexArray(0);

[...]

// ..:: 绘制代码 (in Game loop) :: ..

// 5. 绘制物体

glUseProgram(shaderProgram);

glBindVertexArray(VAO);

someOpenGLFunctionThatDrawsOurTriangle();

glBindVertexArray(0);

绘制

glUseProgram(shaderProgram);

glBindVertexArray(VAO);

glDrawArrays(GL_TRIANGLES, 0, 3);

glBindVertexArray(0);

所有代码

#include<iostream>

// Include GLEW

#include <GL/glew.h>

// Include GLFW

#include <glfw3.h>

GLFWwindow* window;

// Function prototypes

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);

// Window dimensions

const GLuint WIDTH = 800, HEIGHT = 600;

// Shaders

const GLchar* vertexShaderSource = "#version 330 core\n"

"layout (location = 0) in vec3 position;\n"

"void main()\n"

"{\n"

"gl_Position = vec4(position.x, position.y, position.z, 1.0);\n"

"}\0";

const GLchar* fragmentShaderSource = "#version 330 core\n"

"out vec4 color;\n"

"void main()\n"

"{\n"

"color = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"

"}\n\0";

// The MAIN function, from here we start the application and run the game loop

int main()

{

	// Init GLFW

	glfwInit();

	// Set all the required options for GLFW

	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);

	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);

	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

	// Create a GLFWwindow object that we can use for GLFW's functions

	GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr);

	glfwMakeContextCurrent(window);

	// Set the required callback functions

	glfwSetKeyCallback(window, key_callback);

	// Set this to true so GLEW knows to use a modern approach to retrieving function pointers and extensions

	glewExperimental = GL_TRUE;

	// Initialize GLEW to setup the OpenGL Function pointers

	glewInit();

	// Define the viewport dimensions

	int width, height;

	glfwGetFramebufferSize(window, &width, &height);

	glViewport(0, 0, width, height);

	// Build and compile our shader program

	// Vertex shader

	GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);

	glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);

	glCompileShader(vertexShader);

	// Check for compile time errors

	GLint success;

	GLchar infoLog[512];

	glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);

	if (!success)

	{

		glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);

		std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;

	}

	// Fragment shader

	GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);

	glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);

	glCompileShader(fragmentShader);

	// Check for compile time errors

	glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);

	if (!success)

	{

		glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);

		std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;

	}

	// Link shaders

	GLuint shaderProgram = glCreateProgram();

	glAttachShader(shaderProgram, vertexShader);

	glAttachShader(shaderProgram, fragmentShader);

	glLinkProgram(shaderProgram);

	// Check for linking errors

	glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);

	if (!success) {

		glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);

		std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;

	}

	glDeleteShader(vertexShader);

	glDeleteShader(fragmentShader);

	// Set up vertex data (and buffer(s)) and attribute pointers

	GLfloat vertices[] = {

		-0.5f, -0.5f, 0.0f, // Left

		0.5f, -0.5f, 0.0f, // Right

		0.0f, 0.5f, 0.0f  // Top

	};

	GLuint VBO, VAO;

	glGenVertexArrays(1, &VAO);

	glGenBuffers(1, &VBO);

	// Bind the Vertex Array Object first, then bind and set vertex buffer(s) and attribute pointer(s).

	glBindVertexArray(VAO);

	glBindBuffer(GL_ARRAY_BUFFER, VBO);

	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);

	glEnableVertexAttribArray(0);

	glBindBuffer(GL_ARRAY_BUFFER, 0); // Note that this is allowed, the call to glVertexAttribPointer registered VBO as the currently bound vertex buffer object so afterwards we can safely unbind

	glBindVertexArray(0); // Unbind VAO (it's always a good thing to unbind any buffer/array to prevent strange bugs)

	// Game loop

	while (!glfwWindowShouldClose(window))

	{

		// Check if any events have been activiated (key pressed, mouse moved etc.) and call corresponding response functions

		glfwPollEvents();

		// Render

		// Clear the colorbuffer

		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);

		glClear(GL_COLOR_BUFFER_BIT);

		// Draw our first triangle

		glUseProgram(shaderProgram);

		glBindVertexArray(VAO);

		glDrawArrays(GL_TRIANGLES, 0, 3);

		glBindVertexArray(0);

		// Swap the screen buffers

		glfwSwapBuffers(window);

	}

	// Properly de-allocate all resources once they've outlived their purpose

	glDeleteVertexArrays(1, &VAO);

	glDeleteBuffers(1, &VBO);

	// Terminate GLFW, clearing any resources allocated by GLFW.

	glfwTerminate();

	return 0;

}

// Is called whenever a key is pressed/released via GLFW

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)

{

	if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)

		glfwSetWindowShouldClose(window, GL_TRUE);

}

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步骤